System and method for calibrating a light color sensor

ABSTRACT

A method and an ambient light color sensor adapted to determine color of ambient light comprising a memory, a processor, and a light color sensor with a plurality of channels that detect light at different wavelengths. Wherein the memory comprises a calibration matrix determined by calibrating a test light color sensing device under at least one ambient lighting condition, and a normalized gain value for each channel determined by calibrating the ambient light color sensing device to an artificial light source. Wherein the processor receives the sensor readings from the light color sensor, normalizes each received sensor reading using the normalized gain value of a respective channel, determines at least one measured light color value that quantifies color of light from the normalized sensor readings, and determines at least one calibrated light color value by correlating the at least one measured light color value through the calibration matrix.

BACKGROUND OF THE INVENTION Technical Field

Aspects of the embodiments relate to a light color sensor adapted todetect the color, or more particularly the color temperature, of ambientlight, including systems, methods, and modes for calibrating the lightcolor sensor.

Background Art

The lighting industry is starting to better understand the value inmanipulating the color, or more particularly the color temperature, oflight. Color temperature is a description of the warmth or coolness of alight source typically expressed in Kelvins (K)—with a range of betweenabout 2000K (warm colors) to above 5500K (cool colors). Manipulation ofartificial light as the primary circadian stimulus in buildings is now ahot trend in architectural lighting. All plants and animals have abiological clock that tells them when to wake and when to sleep, when tobe alert and when to rest. This internal clock does not exactly measurethe length of an astronomical 24-hour day. Instead, to keep ourcircadian rhythm in sync or entrained with an earthly day, the humanbody is sensitive to environmental stimuli, the most influential beingthe sunlight.

Medical research has identified various circadian rhythm disruptions,typically related to sleep, such as Delayed Sleep Phase Disorder (nightowls), Advanced Sleep Phase Disorder (morning larks), Jet Lag, ShiftWork Disorder, Non-24 (blind people getting day and night mixed up), andNarcolepsy. These, along with other health and wellbeing concerns, haveput circadian rhythm and the non-visual effects of light at theforefront of the architectural lighting design community. Lighting canstimulate our circadian system to invoke entrainment or acute alertnessin the architectural spaces we build. Quantitative metrics, such as theCircadian Stimulus (CS), help lighting designers collaborate withmedical research to leverage manipulation of artificial light as theprimary circadian stimulus in healthier well buildings.

When designing a space for circadian effect there are various objectivestypically considered for a lighting system, including incident angle(the direction from which light enters the eye), spectrum (the color oflight), intensity (how bright or dark the light is), and dosage (thefrequency and duration of light exposure). Studies have suggested thatchanges of color temperature plays a major role in regulating theinternal circadian rhythm, without which the internal clock can becomeout of alignment. Light intensity also affects the circadian rhythm andmust be taken into consideration. As such, color and light intensityshould be combined to provide a space that is not only safe andefficient, but also satisfies the circadian objectives.

Considerable adjustments and tuning must be made to achieve or modify acircadian objective. Providing a solution that customers can easilyunderstand and use is paramount. A typical implementation of a circadiansolution includes a color changing luminaire, a controller or a controlprocessor, and a user interface that is flexible and easy to use. Toproperly design for spectrum, or color, the lighting luminaire containsan array of a plurality of light emitting diodes (LED) and a properlypaired LED driver. The LED array may be a tunable white array (i.e.2200K-6000K) or a full red-green-blue-white (RGB(W)) chipset. The LEDdriver may be digitally addressable via digital control protocols, suchas DMX or DALI®, to more accurately reproduce color and light intensity.The color of a fixture may be also controlled using a 0-10V, phase (dimto warm), or PWM (tape lights) signals. Typically, end users areprovided with graphical user interfaces (GUIs), such as touch screens,mobile apps, or desktop apps, for manual adjustment of color temperatureas well as light intensity. For example, color temperature can beadjusted using color pickers by typing in the RGB value or Kelvinsliders to select a color by touch. However, such interfaces may becomeconfusing and prone to human error. While a desired color temperaturecan be selected, this color temperature may not be optimal in achievinga circadian objective.

On the other hand, automatically adjusting the color temperature andintensity of light to synchronize with the natural circadian rhythm cancreate an optimal environment. In office spaces, circadian lightingcontrol can help drive greater concentration, productivity, andcreativity among workers. In healthcare environments, such as in apatient's room, it can promote faster healing, which translates intobetter outcomes, faster patient out-time, and cost savings. Inclassrooms, it can lead to better student behavior and concentration.And in hotels it can help guests acclimate their natural body rhythms tolocal time and thereby mitigate the effects of jet lag during the day.In addition to the physical benefits, the new WELL Building Standard®provides building owners and managers cost-saving deployment guidelinesfor building features that impact health and wellbeing, includinglighting.

Accordingly, a need has arisen for systems, methods, and modes for alight color sensor that can automatically control the color, or moreparticularly the color temperature, of a lighting system based onnatural sunlight readings.

SUMMARY OF THE INVENTION

It is an object of the embodiments to substantially solve at least theproblems and/or disadvantages discussed above, and to provide at leastone or more of the advantages described below.

It is therefore a general aspect of the embodiments to provide systems,methods, and modes for a light color sensor that can automaticallycontrol color, or more particularly the color temperature, of a lightingsystem based on natural sunlight readings.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

Further features and advantages of the aspects of the embodiments, aswell as the structure and operation of the various embodiments, aredescribed in detail below with reference to the accompanying drawings.It is noted that the aspects of the embodiments are not limited to thespecific embodiments described herein. Such embodiments are presentedherein for illustrative purposes only. Additional embodiments will beapparent to persons skilled in the relevant art(s) based on theteachings contained herein.

DISCLOSURE OF INVENTION

According to one aspect of the embodiments, an ambient light colorsensor is provided adapted to determine color of ambient light. Thesensor comprises a sensor body comprising at least one diffuser and alight color sensing module disposed below the at least one diffuser. Thelight color sensing module comprises a plurality of channels adapted todetect light collected by the at least one diffuser at differentwavelengths to produce sensor readings. The sensor is adapted to: storea calibration matrix determined by calibrating a test light color sensorto a test ambient light source; receive the sensor readings from thelight color sensing module; determine an interpolated spectral powerdistribution from the received sensor readings; convert the interpolatedspectral power distribution to at least one measured light color valuethat quantifies color of light; and determine at least one calibratedlight color value by correlating the at least one measured light colorvalue through the calibration matrix.

According to an embodiment, the calibration matrix correlates testsensor readings of the test ambient light source determined by the testlight color sensor with target sensor readings of the test ambient lightsource determined by a spectrometer. According to a further embodiment,the calibration matrix is developed by testing the test ambient lightsource under different ambient lighting conditions. The ambient lightingconditions may comprise different times of day, different times of year,on a sunny day with clear sky under direct sunlight, on a sunny day withclear sky but indirectly in the shade, during a cloudy day, and anycombinations thereof. According to an embodiment, the test light colorsensor comprises substantially the same components as the ambient lightcolor sensor. According to another embodiment, the ambient light colorsensor is the test light color sensor.

According to a further embodiment, the calibration matrix is determinedby a test processor adapted to: receive test sensor readings of theambient light source from the test light color sensor; determine a testinterpolated spectral power distribution from the received test sensorreadings; convert the test interpolated spectral power distribution toat least one test light color value that quantifies color of light; anddetermine the calibration matrix by correlating the at least one testlight color value to at least one target light color value, wherein theat least one target light color value is determined from target sensorreadings of the ambient light source by a spectrometer. According to anembodiment, the test light color sensor may comprise at least oneprocessor adapted to store a test normalized gain value for each channelof the test light color sensor and normalize each received test sensorreading of the test light color sensor using the test normalized gainvalue of a respective channel, wherein each test normalized gain valueis determined by calibrating the test light color sensor to anartificial light source. According to an embodiment, the at least oneprocessor of the ambient light color sensor may be further adapted tostore a normalized gain value for each channel and normalize eachreceived sensor reading of the ambient light color sensor using thenormalized gain value of a respective channel, wherein each normalizedgain value is determined by calibrating the ambient light color sensorto the artificial light source.

According to an embodiment, the sensor readings received from theambient light color sensor and test sensor readings received from thetest light color sensor during calibration thereof may be normalized bycalibrating the ambient light color sensor and the test light colorsensor to an artificial light source. According to an embodiment, the atleast one processor of the ambient light color sensor may be furtheradapted to store a normalized gain value for each channel and normalizeeach received sensor reading using the normalized gain value of arespective channel, wherein each normalized gain value is determined bycalibrating the ambient light color sensor to an artificial lightsource. According to an embodiment, the normalized gain values aredetermined by a test processor adapted to: store a target representationof a spectral power distribution of the artificial light source; receivetest sensor readings of the artificial light source from the ambientlight color sensor; determine a test representation of spectral powerdistribution of the artificial light source using the test sensorreadings; and determine the normalizing gaining values by comparing thetest representation of spectral power distribution of the artificiallight source to the target representation of the spectral distributionof the artificial light source. According to an embodiment, the targetrepresentation of the spectral power distribution of the artificiallight source may be determined from sensor readings of the artificiallight source by a spectrometer. According to an embodiment, theartificial light source may comprise a substantially linear spectralpower distribution. The test representation of spectral powerdistribution of the artificial light source may comprise a test slope,and the target representation of the spectral distribution of theartificial light source may comprise a target slope.

According to an embodiment, the received sensor readings may comprisecalibrated module sensor readings obtained by multiplying raw sensorreadings from each channel of the ambient light color sensor module by amodule gain value for the respective channel. The module gain value foreach channel may be determined by calibrating the light color sensormodule to an artificial light source outside of the sensor body.

According to an embodiment, the light color sensor module comprises asix-channel multi-spectral sensor. According to an embodiment, the atleast one calibrated light color value may comprise a correlated colortemperature value, x,y values, XYZ values, RGB values, HSV, and anycombinations thereof. According to an embodiment, the interpolatedspectral power distribution may be determined by using a natural cubicspline interpolation.

According to another aspects of the present embodiments, an ambientlight color sensor is provided adapted to determine color of ambientlight. The sensor comprises a sensor body comprising at least onediffuser, a light color sensing module disposed below the at least onediffuser, and at least one processor. The light color sensing modulecomprises a plurality of channels adapted to detect light collected bythe at least one diffuser at different wavelengths to produce sensorreadings. The at least one processor is adapted to: store a calibrationmatrix that correlates test sensor readings of a test ambient lightsource determined by a test light color sensor with target sensorreadings of the test ambient light source determined by a spectrometer;receive sensor readings from the light color sensing module; determinean interpolated spectral power distribution from the sensor readingsreceived from the light color sensing module; convert the interpolatedspectral power distribution to at least one measured light color valuethat quantifies color of light; and determine at least one calibratedlight color value by correlating the at least one measured light colorvalue through the calibration matrix. The sensor readings received fromthe ambient light color sensor and the test sensor readings receivedfrom the test light color sensor during calibration thereof arenormalized by calibrating the ambient light color sensor and the testlight color sensor to an artificial light source.

According to yet another aspect of the embodiments, a method is providedof calibrating an ambient light color sensor to determine color ofambient light. The ambient light color sensor comprises a sensor bodyhaving at least one diffuser, and a light color sensing module disposedbelow the at least one diffuser. The light color sensing modulecomprises a plurality of channels adapted to detect light collected bythe at least one diffuser at different wavelengths. The method comprisesthe steps of: determining a calibration matrix by calibrating a testlight color sensor to a test ambient light source; storing thecalibration matrix at the ambient light color sensor; receiving sensorreadings from the light color sensing module; determining aninterpolated spectral power distribution from the received sensorreadings; converting the interpolated spectral power distribution to atleast one measured light color value that quantifies color of light; anddetermining at least one calibrated light color value by correlating theat least one measured light color value through the calibration matrix.

According to an embodiment, the step of determining a calibration matrixcomprises the steps of: receiving test sensor readings of the ambientlight source from the test light color sensor; determining a testinterpolated spectral power distribution from the received test sensorreadings; converting the test interpolated spectral power distributionto at least one test light color value that quantifies color of light;determining at least one target light color value from target sensorreadings of the ambient light source by a spectrometer; and determiningthe calibration matrix by correlating the at least one test light colorvalue to the at least one target light color value. According to anotherembodiment the method may further comprise the step of: normalizing thesensor readings received from the ambient light color sensor and testsensor readings received from the test light color sensor duringcalibration thereof by calibrating the ambient light color sensor andthe test light color sensor to an artificial light source. According toanother embodiment, the method may further comprise the steps of:determining a normalized gain value for each channel of the ambientlight color sensor by calibrating the ambient light color sensor to anartificial light source; and normalizing each received sensor reading ofthe ambient light color sensor using the normalized gain value of arespective channel. According to a further embodiment, the step ofdetermining the normalized gain values may further comprise the stepsof: storing a target representation of a spectral power distribution ofthe artificial light source; receiving test sensor readings of theartificial light source from the ambient light color sensor; determininga test representation of spectral power distribution of the artificiallight source using the test sensor readings; and determining thenormalizing gaining values by comparing the test representation ofspectral power distribution of the artificial light source to the targetrepresentation of the spectral distribution of the artificial lightsource.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the embodiments will becomeapparent and more readily appreciated from the following description ofthe embodiments with reference to the following figures. Differentaspects of the embodiments are illustrated in reference figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be considered to be illustrative rather than limiting. Thecomponents in the drawings are not necessarily drawn to scale, emphasisinstead being placed upon clearly illustrating the principles of theaspects of the embodiments. In the drawings, like reference numeralsdesignate corresponding parts throughout the several views.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a lighting control system comprising a light colorsensor according to an embodiment.

FIG. 2 illustrates a block diagram of the light color sensor accordingto an embodiment.

FIG. 3 illustrates an exploded view of the light color sensor accordingto an embodiment.

FIG. 4 illustrates a cross-sectional view of the light color sensor andits position with respect to sunlight according to an embodiment.

FIG. 5 shows a flowchart illustrating the steps for a method ofcalibrating the light color sensor according to an embodiment.

FIG. 6 shows a flowchart illustrating the steps for a method ofcalibrating the light color sensor to determine a normalizing gain valueaccording to an embodiment.

FIG. 7 illustrates a diagram of a test fixture for calibrating the lightcolor sensor according to an embodiment.

FIG. 8 illustrates an exemplary spectral power distribution of a halogenlamp.

FIG. 9 shows a flowchart illustrating the steps for a method ofcalibrating the light color sensor to determine a calibration matrixaccording to an embodiment.

FIG. 10 illustrates an exemplary set of the six channel sensor readingson a spectral power distribution graph.

FIG. 11 illustrates an exemplary interpolated spectral powerdistribution of the six channel sensor readings shown in FIG. 10.

FIG. 12 shows the CIE XYZ standard observer color matching functions.

FIG. 13 shows a flowchart illustrating the steps for a method executedby the light color sensor to measure a color, and more particularly thecolor temperature, of light according to an embodiment.

FIG. 14 shows an x, y chromaticity space with the Planckian locusblack-body curve.

FIG. 15 illustrates an exemplary spectral power distribution of typicaldaylight.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments are described more fully hereinafter with reference tothe accompanying drawings, in which embodiments of the inventive conceptare shown. In the drawings, the size and relative sizes of layers andregions may be exaggerated for clarity. Like numbers refer to likeelements throughout. The embodiments may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the inventive concept to those skilled in the art.The scope of the embodiments is therefore defined by the appendedclaims. The detailed description that follows is written from the pointof view of a control systems company, so it is to be understood thatgenerally the concepts discussed herein are applicable to varioussubsystems and not limited to only a particular controlled device orclass of devices.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with an embodiment is included inat least one embodiment of the embodiments. Thus, the appearance of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout the specification is not necessarily referring to the sameembodiment. Further, the particular feature, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

LIST OF REFERENCE NUMBERS FOR THE ELEMENTS IN THE DRAWINGS IN NUMERICALORDER

The following is a list of the major elements in the drawings innumerical order.

-   -   100 Lighting Control System    -   101 Light Color Sensor    -   104 Lighting Control Device(s)    -   105 Lighting Control Processor    -   106 Lighting Load(s)    -   108 Junction Box    -   110 Interior Space    -   112 Sunlight    -   201 Processor    -   202 Light Color Sensing Module    -   203 Light Intensity Sensing Module    -   205 Memory    -   206 Network Interface    -   209 Visual Indicator    -   210 Power Supply    -   300 Body    -   301 First Housing Portion    -   302 Second Housing Portion    -   303 Printed Circuit Board (PCB)    -   304 First Dome Diffuser    -   305 Threaded Chase-Nipple    -   306 Second Flat Diffuser    -   307 Wire Leads    -   308 a-c O-Rings    -   310 Threads    -   312 a-c Circumferential Channels    -   313 Opening    -   314 Flange    -   315 Holes    -   316 Standoffs/Spacers    -   317 Screws    -   318 Dehumidifier Pads    -   321 Heating Resistors    -   400 Sun/Sunlight    -   401 Sunrise Position    -   402 Midday Position    -   403 Sunset Position    -   410 Horizon Line    -   400 Angle    -   500 Flowchart Illustrating the Steps for a Method of Calibrating        the Light Color Sensor    -   501-503 Steps of Flowchart 500    -   600 Flowchart Illustrating the Steps for a Method of Calibrating        the Light Color Sensor to Determine a Normalizing Gain Value    -   602-614 Steps of Flowchart 600    -   700 Test Fixture    -   701 Light Source    -   702 Testing Computer    -   703 Base    -   704 Processor    -   705 Memory    -   706 Power Source    -   710 Spectrometer    -   800 Spectral Power Distribution of a Halogen Lamp    -   900 Flowchart Illustrating the Steps for a Method of Calibrating        the Light Color Sensor to Determine a Calibration Matrix    -   902-918 Steps of Flowchart 900    -   1000 Spectral Power Distribution Graph    -   1001-1006 Exemplary Set of Six Channel Sensor Readings    -   1100 Exemplary Interpolated Spectral Power Distribution of the        Six Channel Sensor Readings    -   1300 Flowchart Illustrating the Steps for a Method Executed By        the Light Color Sensor to Measure a Color, or more particularly        the Color Temperature, of Light    -   1302-1314 Steps of Flowchart 1300    -   1400 x, y Chromaticity Space    -   1401 Planckian Locus Black-Body Curve    -   1500 Spectral Power Distribution of Typical Daylight.

LIST OF ACRONYMS USED IN THE SPECIFICATION IN ALPHABETICAL ORDER

The following is a list of the acronyms used in the specification inalphabetical order.

-   -   ADC Analog to Digital Converter    -   ASIC Application Specific Integrated Circuits    -   B Blue    -   CAT5 Category 5 Cable    -   CCT Correlated Color Temperature    -   CIE International Commission on Illumination    -   CPU Central Processing Unit    -   ESD Electrostatic Discharge    -   G Green    -   GUI Graphical User Interface    -   HVAC Heating, Ventilation, and Air Conditioning    -   IR Infrared    -   K Kelvins    -   LAN Local Area Network    -   LED Light Emitting Diode    -   lux Luminous Intensity/Luminosity    -   MCU Microcontroller    -   nm Nanometers    -   O Orange    -   PCB Printed Circuit Board    -   PoE Power over Ethernet    -   PMMA Poly(Methyl Methacrylate)    -   PTFE Polytetrafluoroethylene    -   PWM Pulse Width Modulation    -   R Red    -   RAM Random-Access Memory    -   RF Radio Frequency    -   RGB Red-Green-Blue    -   RISC Reduced Instruction Set    -   ROM Read-Only Memory    -   SPD Spectral Power Distribution    -   Tt Total-Light Transmittance    -   UV Ultraviolet    -   V Violet    -   W White    -   Y Yellow

MODE(S) FOR CARRYING OUT THE INVENTION

For 40 years Crestron Electronics, Inc. has been the world's leadingmanufacturer of advanced control and automation systems, innovatingtechnology to simplify and enhance modern lifestyles and businesses.Crestron designs, manufactures, and offers for sale integrated solutionsto control audio, video, computer, and environmental systems. Inaddition, the devices and systems offered by Crestron streamlinestechnology, improving the quality of life in commercial buildings,universities, hotels, hospitals, and homes, among other locations.Accordingly, the systems, methods, and modes of the aspects of theembodiments described herein can be manufactured by CrestronElectronics, Inc., located in Rockleigh, N.J.

The different aspects of the embodiments described herein pertain to thecontext of a light color sensor, but is not limited thereto, except asmay be set forth expressly in the appended claims. Referring to FIG. 1,there is shown a lighting control system 100 comprising a light colorsensor 101 according to an embodiment. The lighting control system 100may be adapted to control one or more lighting loads 106 inside aninterior space 110 and may further comprise a lighting control processor105 and one or more lighting control devices 104. The lighting controlsystem 100 may be installed in any type of interior space, such as anoffice building, conference room, classroom, hospital, retail space,commercial space, residential space, or the like.

According to an embodiment, each lighting load 106 may comprise at leastone color changing light emitting diode (LED) array, such as a tunablewhite (i.e. 2200K-6000K) array or a chipset array with red (R), green(G), blue (B), and white (W) LEDs that can be combined by configuringtheir intensity to produce any desired color of light. The lighting load106 may further comprise an LED driver that controls the LED array toproduce desired color and light intensity. The lighting loads 106 may bewired or be wirelessly connected to the control processor 105 to receivecontrol commands and in response change their lighting output.

According to an embodiment, the light color sensor 101 may be mountedinside or outside a building generally directed at the natural lightsource it meant to measure. For example, the light color sensor 101 maybe mounted outdoors on a roof in an upward orientation facing the sky tomeasure the color as well as the intensity of outdoor ambient light,including direct and indirect natural sunlight 112. Mounting the sensor101 outdoors in direct view of sunlight 112 will allow more accuratelight readings. Accordingly, the sensor 101 needs to withstand extremeweather conditions. The sensor 101 may comprise a threaded chase-nipple305 (FIG. 3) on its underside that may be used to clamp the sensor 101to a surface via a threaded conduit nut (not shown). For example, thesensor 101 may be mounted to an outdoor rated junction box 108 mountedon a building via a conduit knockout and may comprise a plurality ofwire leads 307 (FIG. 3) extending into the junction box 108 to connectthe sensor 101 to the lighting control system 100. Although according toanother embodiment, the light color sensor unit 101 may be mountedinside the spade 110 in direction facing a window or a skylight tosample ambient light through the window.

The light color sensor 101 may be adapted to detect the color of visiblelight in terms of its spectral power distribution and it may be adaptedto output a light color value, for example such a correlated colortemperature (CCT), as well as light intensity value, such as luminosity(lux), of natural ambient light. According to one embodiment, the lightcolor sensor 101 may be directly connected to and directly control thelighting load 106 or it may communicate its output to the LED driver ofthe lighting load that controls the light output of the LED array.According to another embodiment, the light color sensor 101 is adaptedto communicate its output to the control processor 105, a lightingcontrol device 104, such as a dimmer, or another intermediary device,which in turn may use the sensor output to control the lighting loads106. In addition, although the control system 100 discussed herein isadapted to control lighting based on the detected color of an exteriorlight source, the detected color may be also used to control other typesof controllable devices based on outdoor lighting conditions, such asaudiovisual devices, shading devices (e.g., motorized roller shades), aswell as heating, ventilation, and air conditioning (HVAC) devices, amongothers. Furthermore, the light color sensor 101 may be also used todetect color of artificial light sources, or a combination of naturallight and artificial light sources.

The light color sensor 101 of the present embodiments may be used invarious applications. The light color sensor 101 may determine the colorof the outdoor natural light to drive the indoor lighting so as to matchthe color temperatures of the interior space 110 to that of the exteriorlighting conditions. This allows system 100 to maintain the occupants'natural circadian rhythm. This application may also be used fordecorative effects, for example, to fool occupants into believing theyare outside. This will give the effect of a space that's open to theair, even if such a space may not contain any windows. So during noonhours with exterior color temperature of about 5500K, the lighting colortemperature inside may be adjusted to match that. On the other hand, theinterior light color temperature may match the color temperature of anovercast day with a color temperature reading of about 7000K. As aresult, the interior space 110 may look like all of the light is comingfrom the natural lighting source 112 rather than the artificial lightingsource 106.

Another application is to determine the outdoor light color temperatureconditions and manipulate the interior space to maintain consistentluminous power density, for example of a work surface, no matter whatthe outdoor conditions are. In another embodiment, in patient care, forexample, when the outdoor color temperature readings are undesired, theinterior lighting loads 106 may be used to offset that by augmentinginterior lighting to a different temperature to improve patient health.

Referring to FIG. 2, there is shown an illustrative block diagram of thelight color sensor 101 according to an embodiment. Light color sensor101 may include various circuit components configured for detecting thecolor of light, as well as light intensity, and transmitting itsreadings or commands to lighting loads 106 either directly or via othercontrol devices, such as 104 and 105.

Light color sensor 101 may comprise a power supply 210 configured forproviding power to the various circuit components of the light colorsensor 101. In one embodiment, the power supply 210 may comprise abattery, such as a BR2032 coin cell battery. In another embodiment,sensor 101 may be connected to line voltage. Power supply 210 mayfurther comprise one or more power converters and regulators to providepower levels required by the electrical or circuit components, such as abuck regulator. In addition, the power supply 210 may comprise surge,electrostatic discharge (ESD), misfire, and/or similar protectioncomponents or circuits.

Light color sensor 101 can further comprise a processor 201. Theprocessor 201 can represent a central processing unit (CPU), one or moremicroprocessors, “general purpose” microprocessors, a combination ofgeneral and special purpose microprocessors, or application specificintegrated circuits (ASICs). Additionally, or alternatively, theprocessor 201 can include one or more reduced instruction set (RISC)processors, video processors, or related chip sets. The processor 201can provide processing capability to execute an operating system, runvarious applications, and/or provide processing for one or more of thetechniques and functions described herein. The processor 201 can processvarious commands and perform operations, such as interpreting lightcolor and light intensity sensor readings, allowing the light colorsensor 101 to join a communication network, or the like.

Light color sensor 101 can further include one or more memory sources205, such as a main memory and/or a nonvolatile memory. Memory 205 canbe communicably coupled to the processor 201 and can store data andexecutable code. Memory 205 can represent volatile memory such asrandom-access memory (RAM), and/or nonvolatile memory, such as read-onlymemory (ROM), hard disk drive, Flash memory, or the like. Memory 205 canstore data files, software for implementing the functions on the controlprocessor 201, as well as network connection information. According toan embodiment, the memory 205 and processor 201 may be incorporated in asingle microcontroller (MCU).

Light color sensor 101 may further comprise a network interface 206,such as a wired or a wireless interface, configured for bidirectionalcommunication on a communication network with other electronic devices,such as the lighting control device 104, the central control processor105, or the like. A wired interface, for example, may be configured forbidirectional communication with other devices over a wired network. Thewired interface can represent, for example, an Ethernet or a Cresnet®port or wire leads 307 (FIG. 3). Cresnet® provides a network wiringsolution for Crestron® keypads, lighting controls, thermostats, andother devices. The Cresnet® bus offers wiring and configuration,carrying bidirectional communication and 24 VDC power to each deviceover a simple 4-conductor cable. On the other hand, the wirelessinterface can comprise a radio frequency (RF) transceiver, an infrared(IR) transceiver, or other communication technologies known to thoseskilled in the art. The wireless interface may communicate using theinfiNET EX® protocol from Crestron Electronics, Inc. of Rockleigh, N.J.,ZigBee® protocol from ZigBee Alliance, via Bluetooth transmission, orthe like.

In various aspects of the embodiments, the network interface 206 and/orpower supply 210 can comprise a Power over Ethernet (PoE) interface. Thelight color sensor 101 can receive both the electric power signal andtransmit readings or control commands via a communication networkthrough the PoE interface. For example, the PoE interface may beconnected through category 5 cable (CAT5) to a local area network (LAN)which contains both a power supply and multiple control points andsignal generators.

Light color sensor 101 may further comprise a visual indicator 209 todisplay a status of the sensor 101, identity functionality, as well asfor any error reporting for diagnostics. The visual indicator 209 maycomprise one or more LEDs, such as red and green LEDs. The visualindicator 209 may indicate whether the light color sensor 101 is tryingto join a network, when it is configured, or the like.

Light color sensor 101 may comprise a light color sensing module 202adapted for detecting color of visible light regardless of luminance.The light color sensing module 202 may comprise a multichannel spectralsensor, an RGB sensor, an XYZ sensor, or the like. It can measure lightover a wide spectrum and it can either provide narrowband or widebandreadings. For example, the light color sensing module 202 may comprise anarrowband six-channel multi-spectral sensor chipset with sixphotodiodes for sensing separate color components of light and providinganalog channel readings over six channels. The analog channel readingsmay be converted using analog to digital converters (ADCs) into digitalvalues. Although the description herein is described with a reference toa six-channel sensor module, a sensor module with more or less channelsmay be also utilized. The sensor chipset can also comprise one or morefilters, such as Gaussian filters, to control the light entering thesensor array.

Light color sensor 101 may further comprise a light intensity sensingmodule 203 configured for detecting and measuring light intensities.According to an embodiment, the light color sensing module 202 and thelight intensity sensing module 203 may be integrated in the same chipsetcomponent. According to another embodiment, modules 202 and 203 may beseparate components. For example, the light intensity sensing module 203can comprise an internal photocell with 0-65535 lux (0-6089foot-candles) light sensing, such as an open-loop daylight sensor, tomeasures light intensity from natural daylight. Light intensity sensingmodule 203 may monitor natural daylight and output a light intensityreading, for example in a form of a luminous intensity (lux) of theobserved light. Using the readings, the light color sensor 101 cansignal the lighting control system 100 to raise or lower the lightsaccording to natural light fluctuations, reducing energy usage whilemaintaining a consistent light intensity for a more efficient andcomfortable work or living space.

Referring to FIG. 3, there is shown an exploded view of the light colorsensor 101. Light color sensor 101 may comprise a sensor body 300 havinga first housing portion 301 connected to a second housing portion 302via threads 310. According to an embodiment, the sensor body 300 maycomprise a plastic material, such as polytetrafluoroethylene (PTFE), orTeflon®, or equivalent plastic that can withstand outdoor exposure for aprolonged period of time. The color of the sensor body 300 may comprisea natural white color, which allows the body 101 to reflect and notabsorb light and heat. The first housing portion 301 may comprise thethreaded chase-nipple 305 extending from its underside. One or moreo-rings, such as three o-rings 308 a-c, may be compressed within variouscircumferential channels 312 a-b between the first and second housingportions 301 and 302 to provide a water tight seal, as shown in greaterdetail in FIG. 4. The sensor body 300 may house a printed circuit board(PCB) 303, a first dome diffuser 304, and a second flat diffuser 306therein.

The PCB 303 may comprise the various electrical components of the lightcolor sensor 101 as discussed above with reference to FIG. 2, includingthe light color sensing module 202. The light color sensor 101 mayfurther comprise flying leads 307 connected to the backside of the PCB303 and extending through and out of the chase-nipple 305. For example,a Cresnet® connection can be implemented via the flying leads 307 toprovide communications as well as power to the light color sensor 101.According to an embodiment, the PCB 303 may contain the visual indicator209, such as an LED, thereon, which may be visible through the first andsecond diffusers 304 and 306, to maintain the watertight seal. Whenturned on, the dome shaped diffuser 304 may diffuse the light emittedfrom the visual indicator 209 causing the diffuser 304 to light up andprovide visual signal to the user.

The first diffuser 304 may be generally domed in shape and may extendout of the sensor body 300 through an opening 313 in the second housingportion 302 to capture sunlight and direct it to the light color sensingmodule 202 on PCB 303. The dome diffuser 304 may comprise a flange 314configured to be secured between the first hosing portion 301 and thesecond housing portion 302 to retain the first diffuser 304 by thesensor body 300. The shape of the dome diffuser helps capture light fromall angles, which brings in more light to the sensor and provides moreaccurate readings. According to an embodiment, the dome diffuser 304 issufficiently dome shaped in order to gather more incident sunlight fromnear the horizon line. This allows the light color sensor 101 to detectthe color of light more accurately during sunrise and sunset. Referringto FIG. 4, there is shown a cross-sectional view of the light colorsensor 101 according to an embodiment. Because the first diffuser 304 isdome shaped, the sun 400 remains in its view regardless of the skyposition of the sun 400. As shown in FIG. 4, the sun 400 issubstantially incident or normal to the outer surface of the firstdiffuser 304 during the entire travel of the sun 400 from sunrise 401,midday 402, and to sunset 403 positions. As such, the dome diffuser 304can collect light from variety of angles, even when the sun 400 is overthe horizon line 410, thereby increasing the optics on the side of thelight color sensor 101 as it lets light through from a wide area. A flatdiffuser or an insufficiently rounded diffuser, on the other hand, willnot be able to effectively gather sunlight throughout the day.

The dome diffuser 304 may comprise a white diffused material or layerthat is exposed to the sunlight. The dome diffuser 304 may comprise aplastic material, such as polycarbonate, polycarbonate blend,poly(methyl methacrylate) (PMMA), or the like. According to anembodiment, the first diffuser 304 may comprise Panlite® ML-6500ZDLpolycarbonate material available from Teijin Limited. In otherembodiments, a glass material, acrylic glass, or other similar materialscapable of providing sufficient diffusion levels may be utilized. Thediffusion of the first diffuser 304 allows light to refract and reflectrandomly and thereby scatter around and be collected by the domediffuser 304. As such, the diffusion of the first diffuser 304 allowsthe first diffuser 304 to collect natural light, limit glare of the sun,spread light evenly, and reduce hard shadows, thereby preserving thenormal color temperature of the sunlight. Diffusing light, instead offocusing light like lenses, allows the light color sensor 101 togenerate more accurate readings. Using a lens, instead of a domediffuser 304, on the other hand, will focus light, which will produceinaccurate readings. Although in addition to the dome diffuser 304, thelight color sensing module 202 may still contain a lens over it toprovide a light collecting function.

According to one embodiment, the first diffuser may comprise a diffusionlevel of about above 50% (with Total-light transmittance (Tt) at aboutbelow 50%). However, it is difficult to achieve sufficient as well asconsistent diffusion levels throughout the entire surface of a domeshaped diffuser 304 in a cost effective manner. Low diffusion levels donot provide accurate results, while high diffusion levels, for exampleabove 50%, provide better and consistent readings. Materials with highlevels of diffusion that can be molded, such as via injection molding,into or onto a dome shape may be cost prohibitive. A cheaper methodwould be to form a white diffusion layer on the inner surface of thedome diffuser 304. However, this method fails to achieve consistentdiffusion levels throughout the entire surface of a dome shapeddiffuser. For example, thermoforming a plastic diffusion layer withinthe dome diffuser 304 causes the plastic layer to get very thin at thetop as compared to the sides of the dome diffuser 304, losing diffusionconsistency and thereby accuracy of color temperature readings.

Accordingly, the light color sensor 101 may comprises a second diffuser306 positioned underneath the dome diffuser 304—forming a doublediffusion construction. The secondary flat diffuser 306 is adapted tofurther diffuse the light to reduce light concentration and preventinaccurate readings. The second diffuser 306 may comprise a generallyflat shape. The second diffuser 306 may reside over the PCB 303 at adistance using spacers 316 and may contain holes 315 that receive screws317 for mounting the second diffuser 306 and the PCB 303 to the firsthousing portion 301.

According to an embodiment, the second diffuser 306 may comprise asubstantially triangular shape with cutouts to expose heating elements,such as three heating resistors 321, such that the second diffuser 306resides in between and adjacent to the heating resistors 321 withoutcovering them. Heating resistors 321 may be driven by the processor 201to achieve desired heat to prevent ice or snow accumulations on theouter dome diffuser 304, which may cover the view of the light colorsensing module 202 located underneath. However, the second flat diffuser306 may comprise other shapes, such as a circular shape.

The second diffuser 306 may comprise a white or white coated glass orplastic material. According to an embodiment, the second diffuser 306may comprise a polycarbonate material, such as PALSUN® SG Whitepolycarbonate sheet, available from PALRAM Industries Ltd. The seconddiffuser 306 may comprise diffusion levels of above about 50% (withtotal-light transmittance (Tt) at about below 50%). For example, theflat diffuser 306 may comprise 28% Total-light transmittance (Tt).Because the second diffuser 306 is flat, consistent diffusion levels canbe achieved throughout the entire surface of the second diffuser 306 inan effective and relatively inexpensive manner. The flat shaped diffuser306 points towards the dome shaped diffuser 304 and is used to collectthe light collected by the dome shaped diffuser 304. This allows the usea dome diffuser 304 with higher transmittance levels, such as 65%Total-light transmittance (Tt). However, the second flat diffuser 306may be also used with a dome diffuser 304 with lower transmittancelevels to improve color temperature accuracy. Particularly, referring toFIG. 4, the second flat diffuser 306 is also used to collect sunlightthat comes in at a steep angle, such as angle 412, with respect to lightcolor sensing module 202 during sunrise 401 and sunset 403. The seconddiffuser 306 collects the light and directs it down where it is read bythe light color sensing module 202. By further diffusing the incominglight, the second diffuser 306 eliminates any further dark shadows andprevents it from becoming dark or dull. Because the incoming light issufficiently diffused via the double diffusion layers 304 and 306, itsubstantially retains its natural color, which is read by the lightcolor sensing module 202, resulting in substantially accurate readings.

According to an embodiment, the first and/or second diffuser 304/306further comprise materials with weather resistance characteristics.Materials such as polycarbonates and PMMA do not yellow over time likeother plastics and can withstand outdoor conditions. In addition, thefirst and/or second diffuser 304/306 can comprise materials withultraviolet (UV) radiation blocking properties, for example via UVprotection films or co-extruded UV protection layers on one or two sidesof the diffuser. UV radiation blocking properties allow the transmissionof the natural daylight while reflecting the sun's heat due to infraredradiation. This both reduces the deterioration of the diffusersthemselves, as well as reducing the heat buildup in the light colorsensor 101.

In addition, the light color sensor 101 may comprise one or moredehumidifier pads 318 disposed within the sensor body 300 which maycomprise porous material to collect moisture that gets into the unit andprevent the diffusers 304 and 306 from fogging up for more accuratereadings.

The present embodiments further pertain to systems, methods, and modesfor calibrating the light color sensor 101. Referring to FIG. 15, thereis shown a spectral power distribution (SPD) 1500 of CIE StandardIlluminant D65 defined by the International Commission on Illumination(CIE) for a typical daylight at 6504 K. Light is a form ofelectromagnetic energy that may be defined by a spectral powerdistribution, such as SPD 1500, which characterizes how much energy orpower is emitted at each wavelength in the visible light spectrum.Visible light spectrum is the portion range of wavelengths in theelectromagnetic spectrum that is visible to the human eye. A typicalhuman eye responds to wavelengths from about 380 nanometers (nm) toabout 740 nm. Each individual wavelength within the spectrum of visiblelight wavelengths is representative of a particular color, which can begrouped and summarized as follows:

TABLE 1 Color Wavelength Violet 380-450 nm Blue 450-495 nm Green 495-570nm Yellow 570-590 nm Orange 590-620 nm Red 620-750 nmSpectral power distribution of a light contains a substantially completebasic physical data about the light and serves as the starting point forquantitative analyses of color. The human eye perceives white light whenall the wavelengths of the visible light spectrum strike the human eyeat the same time. For example, typical daylight represented by thespectral power distribution 1500 will appear bluish white since it emitsspectral power at all visible wavelengths (between 380 and 700 nm) withhigher relative spectral power at 450 nm, which corresponds to bluelight.

To determine the color of a light source, such as daylight, the lightsource needs to be sampled at various wavelengths to detect the spectralpower distribution of the light. A spectrometer, for example, maycomprise hundreds or thousands of channels each detecting the spectralpower of the light source at a different wavelength such thatsubstantially an entire spectrum can be captured. However, using aspectrometer is cost prohibitive for lighting control in residential orcommercial applications. Lower cost visible light spectrum sensorchipsets available on the market, such as the light color sensing module202, sample only a small number of wavelengths and thus without anyeffective calibration produce inconsistent and inaccurate results. Inaddition, raw spectral sensor readings of visible light spectrum sensorsdo not have much meaning on their own. Accordingly, according to thesystem and method discussed herein, the light color sensing module 202is calibrated to a known light source and processed to resemble ameaningful representation of the color of light.

As discussed above, the light color sensing module 202 can comprise anarrowband multi-spectral sensor comprising six spectral channelsadapted to sense light at six different wavelengths and report sixspectral power values in units of watts per meter. The six visible lightchannels may detect the spectral power of the measured light in thefollowing wavelengths: violet (V) channel at 450 nm, blue (B) channel at500 nm, green (G) channel at 550 nm, yellow (Y) channel at 570 nm,orange (O) channel at 600 nm, and red (R) channel at 650 nm of light,each channel with 40 nm full-width half-max detection. Sensors withlower or higher number of channels may also be implemented, althoughlower number of channels will significantly reduce resolution of thesensor.

According to the present embodiments, the raw sensor readings receivedfrom the light color sensing module 202 may be calibrated using themethods described below and converted to a light color quantifyingvalue(s), such as correlated color temperature (CCT), Lux, x,y, XYZ, orRGB color values. Referring to FIG. 5, there is shown a flowchart 500illustrating the steps for a method of calibrating the light colorsensor 101. In step 501, the light color sensing module 202 may be firstcalibrated to an artificial light source outside of the sensor body 300of the light color sensor 101 to determine and store a module gain valuefor each sensor channel. For example, the light color sensing module 202can be placed in a test fixture having an artificial light source placedat a distance away from light color sensing module 202. For example, theV, B, G, Y, and O channels may be measured using a 5700 K white LEDlight source and the R channel may be measured using an incandescentlight. During testing, the light source may be turned on to shine on thelight color sensing module 202. The test fixture may read each of thesix channels of the module 202, compare the raw sensor reading of eachchannel to test data of the light source, and determine any errors bycomputing a module gain value for that channel. The determined modulegain value of each channel may be recorded in a memory of the lightcolor sensing module 202. Thereafter, when measuring light, the lightcolor sensing module 202 may factor in the stored module gain value foreach channel by multiplying the raw sensor reading by the module gainvalue for the corresponding channel to yield a calibrated module readingfor that channel. According to a further embodiment, in addition to themodule gain value, an offset value may be determined for each channeland accounted for by the light color sensing module 202 to yield thecalibrated module readings. Step 501 is optional and the calibrationmethod of the present embodiments may start at step 502.

In step 502, the light color sensor 101 is calibrated to an artificiallight source with the light color sensing module 202 located within thesensor body 300 to determine and store a normalizing gain value for eachsensor channel according to the method shown in FIG. 6. The normalizinggain value is used to factor out variation between any two light colorsensor units. Particularly, the light color sensor 101 is assembled suchthat the light color sensing module 202 is located below the firstdiffuser 304 and the second diffuser 306. The manufacturing deficienciesof the first and second diffusers 304 and 306 tend to effect the opticsin terms of diffusion of the first and second diffusers 304 and 306 andthereby may alter the final sensor readings of the light color sensingmodule 202 if not accounted for in a calibration process—causingreadings of one sensor unit 101 to be different than another sensor unit101. Such manufacturing deficiencies comprise variations in thecharacteristics and properties of the first and second diffusers 304 and306 and their assembly within the sensor unit 101, such as variations inimpurities, material composition, thickness, diffusion properties,positioning and distance the first and second diffusers 304 and 306 aremounted with respect to each other and with respect to the light colorsensing module 202, or the like. For example, at cooler frequencies,such as 400 nm, the diffuser characteristics may vary the amount theblue color is excited from one sensor unit to another. Withoutcalibrating the light color sensing module 202 within the sensor body300 a plurality of sensors 101 installed within the same space willproduce different sensor readings under the same light conditions.Calibrating light color sensing module 202 within the sensor body 300normalizes these sensor readings to help alleviate any manufacturingdeficiencies in the two light diffusers 304 and 306 used in the finalproduct such that each produced light color sensor 101 will reportsensor readings that closely match one another when placed in the sameexact light conditions. In addition, each channel of the light colorsensing module 202 may be independently calibrated since themanufacturing deficiencies may effect each channel reading differently.

Referring to FIG. 7, the light color sensor 101 may be calibrated usinga test fixture 700. Test fixture 700 may comprise a base 703, anartificial light source 701, and a testing computer 702. Testingcomputer 702 may comprise a processor 704, a memory 705, and a powersource 706. The base 703 may be configured to receive the threadedchase-nipple 305 and the wire leads 307 of the light color sensor 101such that the dome diffuser 304 of the light color sensor 101 faces thelight source 701. The test fixture 700 can further comprise a calibratedspectrometer 710 adapted to read the spectral power distribution of thelight source 701. Spectrometer 710 and base 703 may be adjacently placedas shown in FIG. 7. According to another embodiment, the spectrometer710 may be positioned underneath the base 703 such that the spectrometer710 and base 703 are centered with respect to the light source 701—inpractice the spectrometer 710 may take a reading of the light source 701and then the light color sensor 101 may be placed on base 703 over thespectrometer 710 to take the reading at substantially the same positionwith respect to the light source 701. The light source 701 may bepositioned at a distance from the device to be tested, in this case thelight color sensor 101. The light source 701 may comprise a widebandlamp, such as a halogen lamp, comprising substantially liner spectralpower distribution across the wavelengths of the visible light spectrum.According to another embodiment, light source 701 may comprise othertypes of lamps, such as a xenon lamp, a fluorescent lamp, ceramic metalhalide lamps, or the like. The light source 701 may comprise a singletemperature of about 3200 Kelvin. FIG. 8 illustrates an exemplaryspectral power distribution 800 of a halogen lamp light source 701comprising a substantially linear curve.

Referring to FIGS. 6 and 7, in step 602, the test computer 702 may storea target representation of the spectral power distribution of the testlight source 701. Such representation may comprise a target slope valueand may also comprise a target slope intercept value of the linear curve800 of the spectral power distribution of the linear light source 701.According to one embodiment, the target representation of the spectralpower distribution of the test light source 701 may be determined basedon manufacturing specification of the light source 701 or an initialmeasurement of the light source 701 using the test spectrometer 710.However, when using any artificial light source 701 at production(manufacturing) overtime, the bulb initial brightness may degrade overtime. In a halogen type light source 701, the measured lux output may becontinuously reduced as the filament continues to heat up, burn, andremain turned on for a long duration. This may affect the stability ofthe spectrum of the light source 701, resulting in different sensorreadings depending on when the light source 701 was tested over time. Toalleviate this problem, the test setup spectrometer 710 may be used toconsistently measure and determine the spectral power distribution ofthe light source 701, which can be used by the test computer 702 todetermine an offset value. This offset value can be computed using aninitial spectrum sample of the calibrated artificial light source 701when it is freshly installed, then subtracted with a daily or repeatedtest snapshot of the current sampled spectrum. This offset value can beapplied to the readings of each spectrum channel of the light colorsensing module 202 during the calibration process or it can be used toconsistently update the stored target representation of the spectralpower distribution of the light source 701 to account for itsdegradation over time.

In step 606, the light color sensor 101 is placed within andelectrically connected to the test fixture 700, and particularly to theprocessor 704 and power source 706, to power up the electricalcomponents of the sensor 101 and to receive sensor readings of the lightcolor sensing module 202. In step 606, the light source 701 is turned onto shine on the light color sensor 101. In step 608, the testingcomputer 702 may receive test sensor readings from each of the sixchannels of the light color sensing module 202. These test sensorreadings may be raw sensor readings or they may comprise calibratedmodule sensor readings by multiplying the raw sensor readings by themodule gain value for each sensor channel determined in step 501 of FIG.5 discussed above. Additionally, the light color sensor 101 may obtaintest sensor readings for a convergence period by taking a plurality ofsamples of the sensor readings, for example 10 samples, for robustness.The plurality of the sensor reading samples for each sensor channel maybe captured as calibration data in a buffer of memory 705 of the testfixture 700 and the buffered sensor reading samples may be averaged.Additionally, faulty sensor reading samples that significantly differfrom the other sensor reading samples may be discarded.

Next, the testing computer 702 is adapted to compare the test sensorreadings to the target light output of the light source 701 to determineany errors. According to one embodiment, a one point calibration may beperformed by identifying slope errors and computing a gain value.Particularly, in step 610 the testing computer 702 determines a testrepresentation of the spectral power distribution of the light source701 for each channel. This test representation may comprise a test slopevalue—which represents the slope of the spectral power distribution 800of the artificial light source 701. According to one embodiment, twomeasurements may be taken by the light color sensor 101 at two powerlevels of the light source 701 in order to calculate the test slopevalue. According to another embodiment, where offset errors are small,it could be presumed that the spectral power of the light source 701 atabout 380 nanometers is zero. The computer 702 may turn on the lightsource 701 at about 50% and sample the light color sensor 101 to receivethe test sensor readings. For each sensor channel, the computer 702 maythen compute a test slope value of a linear curve between a zerospectral power value at about 380 nanometers and the received sensorreading for the corresponding channel.

In step 612, the computer 702 may determine a normalizing gain value, orthe amount by which a sensor reading needs to be amplified, for eachsensor channel by comparing the test representation of the spectraldistribution of the artificial light source 701 (e.g., the test slopevalue) to the target representation of the spectral distribution of theartificial light source 701 (e.g., the target slope value). Thisnormalizing gain value may be positive or negative. For a six channellight color sensing module 202, six independent normalizing gain valuesmay be determined. In addition, because of the aforementionedmanufacturing deficiencies, each sensor unit 101 will comprise adifferent normalizing gain value for the same channel wavelength. Then,in step 614, the normalizing gain values may be stored in memory 205 ofthe light color sensor 101. These normalizing gain values may be used bythe light color sensor 101 to amplify the sensor readings to yieldnormalized sensor readings by multiplying the sensor readings for eachchannel by the corresponding normalizing gain value, as furtherdiscussed below.

According to a further embodiment, offset errors may be also accountedfor by determining a normalizing offset value for each sensor channel byusing the stored target slope intercept value of the linear curve 800and determining the offset between the test linear curve and the targetlinear curve 800 of the spectral power distribution of the light source701. These normalizing offset values can be stored in memory 205 and bealso accounted for when measuring light by the light color sensingmodule 202.

Referring back to FIG. 5, in step 503 the light color sensor 101 storesa calibration matrix determined by calibrating a test light color sensorto an ambient light source with the light color sensing module 202within the sensor body 300 according to the method shown in FIG. 9.Since the sensor readings of the light color sensor 101 are normalizedusing the normalizing gain value such that any two sensors 101 willproduce the same readings, only a single test light color sensor unit101 needs to be calibrated to an ambient light source duringmanufacturing to yield a single calibration matrix. This singlecalibration matrix may be uploaded to and stored and used by a pluralityof light color sensor units 101. Without normalizing the sensor readingsin step 502, different calibration matrixes will need to be developedfor each light color sensor unit 101 to account for manufacturingdeficiencies described above—causing significant delays in manufacturingprocess. The normalizing step 502 allows the development of a singlematrix that can be used across a plurality of sensor units. This allowsfor a development of a robust calibration matrix using a vast amount ofsamples taken over a prolonged period of time under different lightingconditions as discussed below. In addition, this allows the calibrationmatrix to be updated to account for any errors or inconsistencies and beuploaded to the sensor units 101 in future via remote firmware updates.As further discussed below, the calibration matrix maps test sensorreadings of an ambient light source determined by the test light colorsensor to that of target sensor readings from a calibrated spectrometer,which produces substantially accurate results since it contains a largeamount of channels. Variations in diffuser plastics can cause specificwavelengths to be stronger or weaker in varying light conditions, whichmay shift the final sensor data result to a cooler or warmer direction.The purpose of this additional calibration is to further ensure that theresulting sensor output is substantially true to the current lightconditions and closely resembles a substantially accurate higher channelcount of a spectrometer when placed in the same location.

Referring to FIG. 9, in step 902, a light color sensor unit 101 isplaced within and connected to a test fixture. This test fixture cancomprise the test fixture 700 shown in FIG. 7, but it may comprise adifferent text fixture. Instead of comprising an artificial lightsource, the test fixture 700 may be placed in an environment to test anambient light source 701—for example by placing the test fixture 700outside to measure direct or indirect sunlight. In step 906 the testfixture 700 receives test sensor readings from each channel of the lightcolor sensing module 202—in this example six sensor readings. Thesesensor readings may be raw sensor readings or they may comprisecalibrated module sensor readings by multiplying the raw sensor readingsby the module gain value for each sensor channel determined in step 501of FIG. 5 discussed above. In step 908, the sensor 101 normalizes thetest sensor readings using the normalizing gain value for each sensorchannel that was determined according to method of FIG. 6. Particularly,the sensor 101 retrieves the normalizing gain values from memory 205 andmultiplies the sensor reading of each sensor channel by the storednormalizing gain values for the respective sensor channel to yieldnormalized sensor readings.

FIG. 10 illustrates an exemplary set of the six channel sensor readings1001-1006 on a spectral power distribution graph 1000, namely at thefollowing wavelengths: 450, 500, 550, 570, 600, and 650 nm. As isapparent lot of data is missing between any two data points. Thus, instep 910, an interpolated spectral power distribution of the lightsource 701 is determined from the normalized sensor readings of eachchannel to construct data points within the known sensor readings1001-1006 to get a full spectrum of the light source 701. According toan embodiment, the normalized sensor readings are normalized using anatural cubic spline interpolation. While linear, Lagrange, or Newtonpolynomial interpolation may also be used, they produce less accurateresults since they would cut off some of the energy present in naturallight. FIG. 11 illustrates an exemplary interpolated spectral powerdistribution 1100 of the six channel sensor readings 1001-1006 shown inFIG. 10. This steps allows the sensor readings to closely match a higherchannel count data sample with smoother and rounded curves and with thegaps between data points substantially accurately filled in. The resultof this computation yields four coefficients in four equations based ona polynomial degree value equal to 3, as follows:

-   -   INPUT: n; x0, x1, . . . , xn, a0=f (x0), a1=f (x1), . . . , an=f        (xn)    -   OUTPUT: aj, bj, cj, dj for j=0, 1, . . . , n−1        Final Equation: S(x)=Sj(x)=aj+bj(x−xj)+cj(x−xj)2+dj(x−xj)3 for        xj≤x≤xj+1.        With this information, the six point spectrum power distribution        (y-axis) is increased to a much larger data set by solving for y        (spectral power) from a chosen set of input wavelengths        (x-axis).

In step 912, the interpolated spectral power distribution values may beconverted to test light color values that quantify the color of light,such as tristimulus values using the CIE standard observer colormatching functions. The CIE standard observer color matching functionsprovide a mathematical relationship between the power distributionwavelengths in electromagnetic visible spectrum and an objectivedescription of the three physiologically perceived colors in human colorvision. The XYZ standard observer uses the red primary, green primary,and the blue primary, expressed as X, Y, and Z, respectively, which arecalled the XYZ tristimulus values. These tristimulus values can be usedto represent any color and are conceptualized as amounts of threeprimary colors in a tri-chromatic, additive color model. FIG. 12illustrates the CIE XYZ standard observer color matching functions thatlead to the XYZ tristimulus values. Other observers, such as the CIE RGBspace, or other RGB color spaces, are defined by other sets of threecolor-matching function that lead to tristimulus values in those otherspaces. This allows the sensor readings to be translated into data thatcan be used to illuminate light via light fixtures 106. These XYZ valuescan also be used to obtain other units of measure, such as the CCT orRGB color representation.

In step 914, the test fixture 700 receives the target light color valuesfrom the spectrometer 710. Then, in step 916, a calibration matrix isdetermined by correlating or mapping the test light color values takenfrom the sensor unit 101 to target light color values taken from thespectrometer 710. Since the spectrometer 710 produces more accurate andrealistic readings, the calibration matrix allows the readings from thesensor unit 101 to more closely represent the sensed light with only asmall number of channels (such as six channels). This allows theproduction of a low cost sensor unit 101 with high resolution.

The calibration matrix is essentially a transformation matrix of thetrue color sampled values (i.e., the test light color values from thesensor) and the absolute color values (i.e., the target light colorvalues using the calibrated reference spectrometer). Therefore, thecalibration matrix creates a relationship between both measurements. Thevalues for the test light color values and the target light color valuesmay be in the XYZ color space. The calibration matrix can comprise asquare 3×3 size matrix. The calibration matrix can be computed using thefollowing formula:K=(T·S ^(T))·(S·S ^(T))⁻¹

where,

-   -   S is the matrix of the test light color values;    -   T is the matrix of the target light color values; and    -   K is the final calibration matrix.        The matrix of the test light color values (S) and the matrix of        the target light color values (S) can comprise the following        matrixes:

$T = {{\begin{pmatrix}X_{1} & \; & X_{n} \\Y_{1} & \ldots & Y_{n} \\Z_{1} & \; & Z_{n}\end{pmatrix}\mspace{14mu} S} = \begin{pmatrix}X_{1} & \; & X_{n} \\Y_{1} & \ldots & Y_{n} \\Z_{1} & \; & Z_{n}\end{pmatrix}}$Each column in each matrix is one sample starting with 1 to n. The threerows in each matrix are the components of the color, in this case XYZ.

According to an embodiment, the light color sensor 101 may be calibratedfor a convergence period to take a plurality of samples of the sensorreadings in step 906 for robustness in determining the calibrationmatrix. To build a comprehensive calibration matrix that properlycaptures the color of natural sunlight, the test light color values andthe target light color values should be obtained by capturing aplurality of samples under different ambient lighting conditions,including, but not limited to, during different times of day (i.e.,during sunrise, midday, and sunset), during different times of year(i.e., summer versus winter), on a sunny day with clear sky under directsunlight, on a sunny day with clear sky but indirectly in the shade,during a cloudy day, or the like. Using these plurality of samples, thecalibration is built overtime. The plurality of the sensor readingsamples for each sensor channel may be captured as calibration data in abuffer of memory 705 of the test fixture 700. Additionally, faultysensor reading samples that significantly differ from the other sensorreading samples may be discarded. The buffered sensor reading samplesmay be averaged and the averaged sensor readings may be used todetermine the calibration matrix. In addition, the final calibrationmatrix can be compiled from a plurality of matrixes each fine-tuned toparticular lighting conditions to increase accuracy.

In step 918, the determined calibration matrix is stored by the sensorunit 101 in memory 205. As discussed above, a single calibration matrixcan be used for all produced sensor units 101 since their data wasnormalized to account for the aforementioned manufacturing deficiencies.

According to yet another embodiment, for a different application,instead of calibrating the light color sensor to ambient light, thecalibration matrix may be obtained by calibrating the light color sensor101 to a different light source it is meant to measure. For example, ifthe light color sensor 101 is meant to detect the light color of aparticular LED light source, it can be calibrated to that LED lightsource according to FIG. 9.

FIG. 13 represents a method executed by the light color sensor 101 tomeasure a color of light, or more particularly its color temperature,when the light color sensor 101 is installed in the field. In step 1301,the light color sensor 101 may receive a command to measure a lightsource. For example, as previously discussed, the light color sensor 101may be installed outdoors to detect the color temperature of sunlight.In step 1302, the light color sensor 101 receives sensor readings fromeach channel of the light color sensing module 202. These sensorreadings may be raw sensor readings or they may comprise calibratedmodule sensor readings by multiplying the raw sensor readings by themodule gain value for each sensor channel determined in step 501 of FIG.5 discussed above. Additionally, the sensor 101 may be configured tocapture a plurality of sensor readings in step 1302 per each sensorchannel. The sensor readings may be stored in an array and the sensor101 may keep a running average of the samples. The averaged sensorreadings for each sensor channel may be then used to determine the finalsensor output.

In step 1304, the sensor 101 normalizes the sensor readings bymultiplying the sensor reading of each sensor channel by the storednormalizing gain values for the respective sensor channel to yieldnormalized sensor readings. In step 1306, the sensor determines aninterpolated spectral power distribution of the light source from thenormalized sensor reading of each channel using a natural cubic splineinterpolation in a similar manner as discussed above. In step 1308, thesensor 110 converts the interpolated spectral power distribution of thelight source to measured light color values that quantify the color oflight, such as the XYZ tristimulus values. In step 1310, the sensor 101correlates the measured light color values through the calibrationmatrix to obtain calibrated light color values.

According to one embodiment, if it is desired to measure the actualcolor hue or tint of natural light or of an artificial light, the sensor101 can output the calibrated light color values, such as XYZtristimulus values. In another embodiment, the calibrated light colorvalues can be outputted as another units of measure that quantify thecolor of light, such as x,y, RGB, HSV, or similar color values. Thesecalibrated light color values can be directly or indirectly used tomodify the light source 106.

On the other hand, according to another embodiment, if the sensor 101 isdesired and set to measure the color temperature of light, in step 1312,the sensor 101 can convert the calibrated light color values to a colortemperature value such as a correlated color temperature (CCT) value.Correlated color temperature is used to represent the chromaticity of awhite light sources. It is defined by the proximity of the lightsource's chromaticity coordinates to a blackbody locus, such as thePlanckian curve, which defines the colors of white light. FIG. 14 showsan x, y chromaticity space 1400 with the Planckian locus 1401,representing color temperatures of an ideal black-body radiator in arange from red to orange to yellow to white to blueish white, eachconventionally expressed in kelvin units. Correlated color temperaturesat lower color temperature levels (between about 2000K-3500K) are called“warm colors” or “warm white” with yellowish white through orange orreddish appearance. Color temperatures at middle color temperaturelevels (between about 4000K-5000K) are called “neutral” or “brightwhite” with more natural white light appearance. On the upper end (above5500 K), color temperatures are referred as “daylight” with a bluishwhite appearance.

The calibrated light color values, such as the XYZ tristimulus values,which may not be equal to the white colors on the Planckian curve 1401,are correlated to the closest value that falls on the Planckian curve,which defines the correlated color temperature. For example, the sensor101 can apply the calibrated XYZ tristimulus values to a mathematicalmethod to obtain the CCT value, such as using Robertson's method or thatof McCamy's cubic approximation formula as follows:CCT(x,y)=−449n ³+3525n ²−6823.3n+5520.33

Finally, in step 1314, the light color sensor 101 may output the colortemperature value. As discussed above, the color temperature value canbe used to control an artificial light source 106, for example to matchinterior light to exterior lighting conditions.

INDUSTRIAL APPLICABILITY

The disclosed embodiments provide a system, software, and a method for alight color sensor. It should be understood that this description is notintended to limit the embodiments. On the contrary, the embodiments areintended to cover alternatives, modifications, and equivalents, whichare included in the spirit and scope of the embodiments as defined bythe appended claims. Further, in the detailed description of theembodiments, numerous specific details are set forth to provide acomprehensive understanding of the claimed embodiments. However, oneskilled in the art would understand that various embodiments may bepracticed without such specific details.

Although the features and elements of aspects of the embodiments aredescribed being in particular combinations, each feature or element canbe used alone, without the other features and elements of theembodiments, or in various combinations with or without other featuresand elements disclosed herein.

This written description uses examples of the subject matter disclosedto enable any person skilled in the art to practice the same, includingmaking and using any devices or systems and performing any incorporatedmethods. The patentable scope of the subject matter is defined by theclaims, and may include other examples that occur to those skilled inthe art. Such other examples are intended to be within the scope of theclaims.

The above-described embodiments are intended to be illustrative in allrespects, rather than restrictive, of the embodiments. Thus theembodiments are capable of many variations in detailed implementationthat can be derived from the description contained herein by a personskilled in the art. No element, act, or instruction used in thedescription of the present application should be construed as criticalor essential to the embodiments unless explicitly described as such.Also, as used herein, the article “a” is intended to include one or moreitems.

Additionally, the various methods described above are not meant to limitthe aspects of the embodiments, or to suggest that the aspects of theembodiments should be implemented following the described methods. Thepurpose of the described methods is to facilitate the understanding ofone or more aspects of the embodiments and to provide the reader withone or many possible implementations of the processed discussed herein.The steps performed during the described methods are not intended tocompletely describe the entire process but only to illustrate some ofthe aspects discussed above. It should be understood by one of ordinaryskill in the art that the steps may be performed in a different orderand that some steps may be eliminated or substituted.

All United States patents and applications, foreign patents, andpublications discussed above are hereby incorporated herein by referencein their entireties.

ALTERNATE EMBODIMENTS

Alternate embodiments may be devised without departing from the spiritor the scope of the different aspects of the embodiments.

What is claimed is:
 1. An ambient light color sensing device adapted todetermine color of ambient light comprising: a light color sensorcomprising a plurality of channels that detect light at differentwavelengths to produce sensor readings; a memory comprising acalibration matrix and a normalized gain value for each channel, whereinthe calibration matrix is determined by calibrating a test light colorsensing device under at least one ambient lighting condition, andwherein each normalized gain value is determined by calibrating theambient light color sensing device to an artificial light source; and atleast one processor, wherein the at least one processor: receives thesensor readings from the light color sensor; normalizes each receivedsensor reading using the normalized gain value of a respective channel;determines at least one measured light color value that quantifies colorof light from the normalized sensor readings; and determines at leastone calibrated light color value by correlating the at least onemeasured light color value through the calibration matrix.
 2. The deviceof claim 1, wherein the normalized gain values are determined by a testprocessor, wherein the test processor: stores a target representation ofa spectral power distribution of the artificial light source; receivestest sensor readings of the artificial light source from the light colorsensor; determines a test representation of spectral power distributionof the artificial light source using the test sensor readings; anddetermines the normalizing gaining values by comparing the testrepresentation of spectral power distribution of the artificial lightsource to the target representation of the spectral distribution of theartificial light source.
 3. The device of claim 2, wherein the targetrepresentation of the spectral power distribution of the artificiallight source is determined from sensor readings of the artificial lightsource by a spectrometer.
 4. The device of claim 2, wherein theartificial light source comprises a substantially linear spectral powerdistribution.
 5. The device of claim 4, wherein the test representationof spectral power distribution of the artificial light source comprisesa test slope, and wherein the target representation of the spectraldistribution of the artificial light source comprises a target slope. 6.The device of claim 1, wherein the processor determines the at least onemeasured light color value from the normalized sensor readings bydetermining an interpolated spectral power distribution from thenormalized sensor readings and converts the interpolated spectral powerdistribution to the at least one measured light color value.
 7. Thedevice of claim 6, wherein the interpolated spectral power distributionis determined by using a natural cubic spline interpolation.
 8. Thedevice of claim 1, wherein the calibration matrix correlates test sensorreadings determined by the test light color sensing device under the atleast one ambient lighting condition with target sensor readingsdetermined by a spectrometer under the at least one ambient lightingcondition.
 9. The device of claim 1, wherein the calibration matrix isdetermined by testing the test light color sensing device underdifferent ambient lighting conditions.
 10. The device of claim 9,wherein the different ambient lighting conditions are selected from thegroup consisting of different times of day, different times of year, ona sunny day with clear sky under direct sunlight, on a sunny day withclear sky but indirectly in the shade, during a cloudy day, and anycombinations thereof.
 11. The device of claim 1, wherein the test lightcolor sensing device comprises substantially the same components as theambient light color sensing device, or the ambient light color sensingdevice is the test light color sensing device.
 12. The device of claim1, wherein the calibration matrix is determined by a test processor,wherein the test processor: receives test sensor readings from a lightcolor sensor of the test light color sensing device under the at leastone ambient lighting condition; determines a test interpolated spectralpower distribution from the received test sensor readings; converts thetest interpolated spectral power distribution to at least one test lightcolor value that quantifies color of light; and determines thecalibration matrix by correlating the at least one test light colorvalue to at least one target light color value, wherein the at least onetarget light color value is determined from target sensor readingsreceived from a spectrometer under the at least one ambient lightingcondition.
 13. The device of claim 12, wherein the calibration matrixcomprises the following formula:K=(T·S ^(T))·(S·S ^(T))⁻¹ where, S is a matrix of the test light colorvalues; T is the matrix of the target light color values; and K is thecalibration matrix.
 14. The device of claim 13, wherein the matrix ofthe test light color values (S) and the matrix of the target light colorvalues (T) comprise the following matrixes: $T = {{\begin{pmatrix}X_{1} & \; & X_{n} \\Y_{1} & \ldots & Y_{n} \\Z_{1} & \; & Z_{n}\end{pmatrix}\mspace{14mu} S} = {\begin{pmatrix}X_{1} & \; & X_{n} \\Y_{1} & \ldots & Y_{n} \\Z_{1} & \; & Z_{n}\end{pmatrix}.}}$
 15. The device of claim 12, wherein the test lightcolor sensing device comprises at least one processor adapted to store atest normalized gain value for each channel of the light color sensor ofthe test light color sensing device and normalize each received testsensor reading using the test normalized gain value of a respectivechannel of the light color sensor of the test light color sensingdevice, wherein each test normalized gain value is determined bycalibrating the test light color sensing device to an artificial lightsource.
 16. The device of claim 1 further comprising a sensor bodyhaving at least one diffuser, wherein the light color sensor is disposedbelow the at least one diffuser and detects the light collected by theat least one diffuser, wherein the received sensor readings comprisecalibrated sensor readings obtained by multiplying raw sensor readingsfrom each channel of the light color sensor by a module gain value forthe respective channel, wherein the module gain value for each channelis determined by calibrating the light color sensor to an artificiallight source outside of the sensor body.
 17. The device of claim 1,wherein the light color sensor comprises a multi-channel multi-spectralsensor.
 18. A method of calibrating an ambient light color sensingdevice to determine color of ambient light, wherein the ambient lightcolor sensing device comprises a light color sensor comprising aplurality of channels that detect light at different wavelengths toproduce sensor readings, wherein the method comprises the steps of:determining a calibration matrix by calibrating a test light colorsensing device under at least one ambient lighting condition;determining a normalized gain value for each channel by calibrating theambient light color sensing device to an artificial light source; andstoring the calibration matrix and the normalized gain values at theambient light color sensing device; receiving sensor readings from thelight color sensor; normalizing each received sensor reading using thenormalized gain value of a respective channel; determining at least onemeasured light color value that quantifies color of light from thenormalized sensor readings; and determining at least one calibratedlight color value by correlating the at least one measured light colorvalue through the calibration matrix.
 19. The method of claim 18,wherein the step of determining the normalized gain values comprises thesteps of: storing a target representation of a spectral powerdistribution of the artificial light source; receiving test sensorreadings of the artificial light source from the light color sensor;determining a test representation of spectral power distribution of theartificial light source using the test sensor readings; and determiningthe normalizing gaining values by comparing the test representation ofspectral power distribution of the artificial light source to the targetrepresentation of the spectral distribution of the artificial lightsource.
 20. The method of claim 18, wherein the step of determining theat least one measured light color value from the normalized sensorreadings comprises the steps of: determining an interpolated spectralpower distribution from the normalized sensor readings; and convertingthe interpolated spectral power distribution to the at least onemeasured light color value.
 21. The method of claim 18, wherein the stepof determining the calibration matrix comprises the steps of: receivingtest sensor readings from a light color sensor of the test light colorsensing device under the at least one ambient lighting condition;determining at least one test light color value that quantifies color oflight from the received test sensor readings; determined at least onetarget light color value from target sensor readings received from aspectrometer under the at least one ambient lighting condition; anddetermining the calibration matrix by correlating the at least one testlight color value to the at least one target light color value.
 22. Themethod of claim 21, wherein the step of determining the at least onetest light color value from the received test sensor readings comprisesthe steps of: determining a test interpolated spectral powerdistribution from the received test sensor readings; and converting thetest interpolated spectral power distribution to the at least one testlight color value.
 23. The method of claim 21 further comprises the stepof: normalizing the test sensor readings of the test light color sensingdevice during calibration thereof by calibrating the test light colorsensing device to the artificial light source.